Backplate for foldable display device and foldable display device including the same

ABSTRACT

A foldable display device comprises a display panel; and a backplate attached to a side of the display panel and including a hard layer and first and second soft layer attached on lower and upper surfaces of the hard layer, respectively, wherein the hard layer has a difference in a distance from a reference line in a center portion and a first edge portion.

CROSS-REFERENCE TO RELATED APPLICATION

The present application claims the benefit of Korean Patent ApplicationNo. 10-2015-0107151 filed in Korea on Jul. 29, 2015, which is herebyincorporated by reference herein in its entirety.

BACKGROUND OF THE INVENTION

Field of the Invention

The disclosure relates to a foldable display device and moreparticularly to a backplate for a foldable display device for preventingdamage during folding-unfolding operation and a foldable display deviceincluding the backplate.

Discussion of the Related Art

As information technology and mobile communication technology have beendeveloped, a display device for displaying a visual image has also beendeveloped. Flat panel display devices, such as a liquid crystal display(LCD) device and an organic light emitting display (OLED) device, aredeveloped and used.

In general, an LCD device includes a liquid crystal panel, which inturn, includes upper and lower substrates and a liquid crystal layertherebetween. The liquid crystal layer is driven by an electric fieldinduced between a pixel electrode and a common electrode to displayimages.

The OLED device includes an emitting diode, which includes an anode, acathode and an organic emitting layer therebetween, and holes andelectrodes respectively from the anode and the cathode are combined andemits the light in the organic emitting layer to display images.

Recently, the needs for a foldable display device, which is fabricatedby using a flexible substrate, are increased. The foldable displaydevice is folded to be portable and is unfolded to display images.Namely, with the foldable display device, the large size image displaycan be provided, and portability of the display device is improved.

FIG. 1 is a schematic cross-sectional view of the related art foldabledisplay device. As shown in FIG. 1, the foldable display device 10includes a display panel 20, a backplate 30 and a cover window 40. Thedisplay panel 20 includes a flexible substrate 22, a display part 24 onthe flexible substrate 22. For example, the flexible substrate 22 may bea polyimide substrate.

When the display panel 20 is an emitting diode panel, the display part24 may include an emitting diode and a thin film transistor (TFT) fordriving the emitting diode. The emitting diode may include an anode,which is connected to the TFT, an organic emitting layer on the anode,and a cathode on the organic emitting layer. In addition, anencapsulation film for preventing moisture penetration may cover theemitting diode.

On the other hand, when the display panel 20 is a liquid crystal panel,the display part 24 may include a thin film transistor (TFT) on theflexible substrate 22, a pixel electrode connected to the TFT, a countersubstrate facing the flexible substrate 22, a common electrode on theflexible substrate 22 or the counter substrate, and a liquid crystallayer between the flexible substrate 22 and the counter substrate. Thedisplay panel 20 may further include a backlight unit.

With a carrier substrate (not shown) attached to a lower surface of theflexible substrate 22, elements such as the TFT are formed on theflexible substrate 22, and the carrier substrate is released to obtainthe flexible display panel 20.

In the flexible display panel 20, since the flexible substrate 22 is toothin, the backplate 30 for supporting the display panel 20 is disposedunder the flexible substrate 22. For example, the backplate 30 may beformed of polyethylene terephthalate (PET) and may be attached to thedisplay panel 20 by an adhesive layer 32.

The cover window 40 is attached to an upper side of the display panel20. The damage on the display panel 20 from outer impacts is preventedby the cover window 40. Although not shown, the cover window 40 may beattached to the display panel 20 by an adhesive layer.

In the related art foldable display device, the PET film having about100 micrometers is used for the backplate 30. When the folding andunfolding operation is repeated in the foldable display device 10, theplastic deformation occurs in the backplate 30 such that the restorationof the folded display device to its original confirmation becomesdifficult.

Namely, as shown in FIGS. 2A and 2B, since there is the plasticdeformation problem in the backplate 30 (of FIG. 1) of the PET film,there are limitations in the folding and unfolding operation of thefoldable display device 10. Namely, the folding and unfoldingcharacteristic of the foldable display device 10 is deteriorated. FIG.2A illustrates the backplate 30 plastic deformed such that the backplate30 does not revert to its original shape when external force is removed.In FIG. 2B shows the result of plastic deformation of the backplate 30after a repeated folding and unfolding where a center portion 54 isplastic deformed downward and two wing portions 52 are plastic deformedupward.

By reducing a thickness of the backplate 30, the plastic deformationproblem in the backplate 30 may be decreased. However, the elasticrestoring energy of the backplate 30 having the reduced thickness isdecreased such that the time for the restoration of the folded displaydevice is increased.

SUMMARY OF THE INVENTION

Embodiments relate to a foldable display device including a displaypanel and a backplate. The backplate is attached to a surface of thedisplay panel to enhance resilience of the foldable display device. Thebackplate includes a first layer of first material having a firstelastic modulus, a second layer of second material having a secondelastic modulus, and a non-flat layer of third material having a thirdelastic modulus higher than the first elastic modulus and the secondelastic modulus. The non-flat layer is between the first layer and thesecond layer.

In one embodiment, the first material is the same as the secondmaterial.

In one embodiment, the non-flat layer has a concave top surface of apredetermined radius of curvature and a convex bottom surface of thepredetermined radius of curvature.

In one embodiment, the non-flat layer has a first inclined portionslanted downward towards a center line of the non-flat layer along whichthe backplate is bent, and a second inclined portion connected to thefirst inclined portion and slanted downwards towards the center.

In one embodiment, the non-flat layer includes a middle portion having aconcave top surface and a convex bottom surface; and edge portions, eachof the edge portions connected to an edge of the middle portion, each ofthe edge portions having a convex top surface and a concave bottomsurface.

In one embodiment, the concave top surface and the convex bottom surfaceof the middle portion are curved, and the convex top surface and theconcave bottom surface of each of the edge portions are curved.

In one embodiment, the concave top surface and the convex bottom surfaceof the middle portion comprise a plurality of flat surfaces, and theconvex top surface and the concave bottom surface of each of the edgeportions comprise a plurality of flat surfaces.

In one embodiment, the first layer has a flat top surface and a convexbottom surface, the flat top surface secured to the display panel andthe convex bottom surface secured to a top surface of the non-flatlayer.

In one embodiment, the first layer has a bottom surface of a profilethat matches a profile of a top surface of the non-flat layer, and thesecond layer has a top surface of a profile that matches a profile of abottom surface of the non-flat layer.

In one embodiment, the non-flat layer has a same thickness at differentportions of the non-flat layer.

In one embodiment, the non-flat layer has a first thickness at a firstlocation of the non-flat layer and a second thickness at a secondlocation of the non-flat layer, the second thickness different from thefirst thickness.

In one embodiment, the non-flat layer is curved or bent towards a shapethat results from plastic deformation of the non-flat layer by repeatedfolding and unfolding of the backplate.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention and are incorporated in and constitute apart of this specification, illustrate embodiments of the invention andtogether with the description serve to explain the principles of theinvention.

FIG. 1 is a schematic cross-sectional view of a foldable display devicein related art.

FIGS. 2A and 2B are views showing a plastic deformation issue in thebackplate of related art.

FIG. 3A is a schematic cross-sectional view of a foldable display deviceaccording to an embodiment.

FIG. 3B is a schematic cross-sectional view of a backplate according toan embodiment of FIG. 3A.

FIGS. 4A and 4B are schematic cross-sectional views of display panelsaccording to embodiments.

FIG. 5A is a schematic cross-sectional view of a foldable display deviceaccording to an embodiment.

FIG. 5B is a schematic cross-sectional view of a backplate according tothe embodiment of FIG. 5A.

FIG. 6A is a schematic cross-sectional view of a foldable display deviceaccording to an embodiment.

FIG. 6B is a schematic cross-sectional view of a backplate according tothe embodiment of FIG. 6A.

FIG. 7A is a schematic cross-sectional view of a foldable display deviceaccording to an embodiment.

FIG. 7B is a schematic cross-sectional view of a backplate according tothe embodiment of FIG. 7A.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Reference will now be made in detail to the preferred embodiments,examples of which are illustrated in the accompanying drawings.

FIG. 3A is a schematic cross-sectional view of a foldable display deviceaccording to an embodiment, and FIG. 3B is a schematic cross-sectionalview of a backplate according to the embodiment of FIG. 3B.

As shown in FIGS. 3A and 3B, a foldable display device 100 includes adisplay panel 110, a backplate 180, which is disposed under the displaypanel 110 and includes a first soft layer 182, a hard layer 184 (alsoreferred to as a “non-flat layer” herein) and a second soft layer 186,and a cover window 190 disposed on the display panel 110. The displaypanel 110 includes a flexible substrate 112 and a display part 114 onthe flexible substrate 112. For example, the flexible substrate 112 maybe a polyimide substrate.

The process of forming the display part 114 is performed on the flexiblesubstrate 112 while the flexible substrate 112 is attached to a carriersubstrate (not shown) such as a glass substrate. After the process offorming the display part 114, the carrier substrate and the flexiblesubstrate 112 are separated or released to obtain the display panel 110.

A shown in FIGS. 3A and 3B, the center portion 183 of the hard layer 184is curved downward. As shown in FIG. 2B, downward plastic deformationtends to appear along the center portion of the back cover 30.Therefore, the hard layer 184 is pre-formed with downward curve in thecenter portion 183 so as to prevent downward plastic deformation fromoccurring.

FIGS. 4A and 4B are schematic cross-sectional views of display panelaccording to an embodiment. As shown in FIG. 4A, the display panel 110may be an emitting diode panel.

A buffer layer 120 is formed on the flexible substrate 112, and a thinfilm transistor (TFT) Tr is formed on the buffer layer 120. The bufferlayer 120 may be omitted.

A semiconductor layer 122 is formed on the buffer layer 120. Thesemiconductor layer 122 may include an oxide semiconductor material orpolycrystalline silicon. When the semiconductor layer 122 includes theoxide semiconductor material, a light-shielding pattern (not shown) maybe formed under the semiconductor layer 122. The light to thesemiconductor layer 122 is shielded or blocked by the light-shieldingpattern such that thermal degradation of the semiconductor layer 122 canbe prevented. On the other hand, when the semiconductor layer 122includes polycrystalline silicon, impurities may be doped into bothsides of the semiconductor layer 122.

A gate insulating layer 124 is formed on the semiconductor layer 122.The gate insulating layer 124 may be formed of an inorganic insulatingmaterial such as silicon oxide or silicon nitride.

A gate electrode 130, which is formed of a conductive material, e.g.,metal, is formed on the gate insulating layer 124 to correspond to acenter of the semiconductor layer 122.

In FIG. 4A, the gate insulating layer 124 is formed on the entiresurface of the flexible substrate 112. Alternatively, the gateinsulating layer 124 may be patterned to have the same shape as the gateelectrode 130.

An interlayer insulating layer 132, which is formed of an insulatingmaterial, is formed on an entire surface of the flexible substrate 112including the gate electrode 130. The interlayer insulating layer 132may be formed of an inorganic insulating material, e.g., silicon oxideor silicon nitride, or an organic insulating material, e.g.,benzocyclobutene or photo-acryl.

The interlayer insulating layer 132 includes first and second contactholes 134 and 136 exposing both sides of the semiconductor layer 122.The first and second contact holes 134 and 136 are positioned at bothsides of the gate electrode 130 to be spaced apart from the gateelectrode 130.

In FIG. 4A, the first and second contact holes 134 and 136 extend intothe gate insulating layer 124. Alternatively, when the gate insulatinglayer 124 is patterned to have the same shape as the gate electrode 130,there may be no first and second contact holes 134 and 136 in the gateinsulating layer 124.

A source electrode 140 and a drain electrode 142, which are formed of aconductive material, e.g., metal, are formed on the interlayerinsulating layer 132. The source electrode 140 and the drain electrode142 are spaced apart from each other with respect to the gate electrode130 and respectively contact both sides of the semiconductor layer 122through the first and second contact holes 134 and 136.

The semiconductor layer 122, the gate electrode 130, the sourceelectrode 140 and the drain electrode 142 constitute the TFT Tr, and theTFT Tr serves as a driving element.

In FIG. 4A, the gate electrode 130, the source electrode 140 and thedrain electrode 142 are positioned over the semiconductor layer 122.Namely, the TFT Tr has a coplanar structure. Alternatively, in the TFTTr, the gate electrode may be positioned under the semiconductor layer,and the source and drain electrodes may be positioned over thesemiconductor layer such that the TFT Tr may have an inverted staggeredstructure. In this instance, the semiconductor layer may includeamorphous silicon.

Although not shown, a gate line and a data line are disposed on or overthe flexible substrate 112 and cross each other to define a pixelregion. In addition, a switching element, which is electricallyconnected to the gate line and the data line, may be disposed on theflexible substrate 112. The switching element is electrically connectedto the TFT Tr as the driving element.

In addition, a power line, which is parallel to and spaced apart fromthe gate line or the data line, may be formed on or over the flexiblesubstrate 112. Moreover, a storage capacitor for maintaining a voltageof the gate electrode 130 of the TFT Tr during one frame, may be furtherformed on the flexible substrate 112.

A passivation layer 150, which includes a drain contact hole 152exposing the drain electrode 142 of the TFT Tr, is formed to cover theTFT Tr.

A first electrode 160, which is connected to the drain electrode 142 ofthe TFT Tr through the drain contact hole 152, is separately formed ineach pixel region. The first electrode 160 may be an anode and may beformed of a conductive material having a relatively high work function.For example, the first electrode 160 may be formed of a transparentconductive material such as indium-tin-oxide (ITO) or indium-zinc-oxide(IZO).

When the display panel 110 is operated in a top-emission type, areflection electrode or a reflection layer may be formed under the firstelectrode 160. For example, the reflection electrode or the reflectionlayer may be formed of aluminum-paladium-copper (APC) alloy.

A bank layer 166, which covers edges of the first electrode 160, isformed on the passivation layer 150. A center of the first electrode 160in the pixel region is exposed through an opening of the bank layer 166.

An organic emitting layer 162 is formed on the first electrode 160. Theorganic emitting layer 162 may have a single-layered structure of anemitting material layer formed of an emitting material. Alternatively,to improve emitting efficiency, the organic emitting layer 162 may havea multi-layered structure including a hole injection layer, a holetransporting layer, the emitting material layer, an electrontransporting layer and an electron injection layer sequentially stackedon the first electrode 160.

A second electrode 164 is formed over the flexible substrate 112including the organic emitting layer 162. The second electrode 164 ispositioned at an entire surface of the display area. The secondelectrode 164 may be a cathode and may be formed of a conductivematerial having a relatively low work function. For example, the secondelectrode 164 may be formed of aluminum (Al), magnesium (Mg) or Al—Mgalloy.

The first electrode 160, the organic emitting layer 162 and the secondelectrode 164 constitute the light emitting diode D. An encapsulationfilm 170 is formed on the light emitting diode D to prevent penetrationof moisture into the light emitting diode D.

The encapsulation film 170 may have has a triple-layered structure of afirst inorganic layer 172, an organic layer 174 and a second inorganiclayer 176. However, it is not limited thereto.

A polarization plate (not shown) may be disposed on the encapsulationfilm 170 to reduce an ambient light reflection. The polarization platemay be a circular polarization film.

On the other hand, as shown in FIG. 4B, a liquid crystal panel 210 maybe used for the display panel 110. The liquid crystal panel 210 includesfirst and second flexible substrates 212 and 250, which face each other,and a liquid crystal layer 260, which includes liquid crystal molecules262, therebetween.

A first buffer layer 220 is formed on the first flexible substrate 212,and a TFT Tr is formed on the first buffer layer 212. The first bufferlayer 220 may be omitted.

A gate electrode 222 is formed on the first buffer layer 220, and a gateinsulating layer 224 is formed on the gate electrode 222. In addition, agate line (not shown), which is connected to the gate electrode 222, isformed on the first buffer layer 220.

A semiconductor layer 226 corresponding to the gate electrode 222 isformed on the gate insulating layer 224. The semiconductor layer 226 mayinclude an oxide semiconductor material. Alternatively, thesemiconductor layer may include an active layer of intrinsic amorphoussilicon and an ohmic contact layer of impurity-doped amorphous silicon.

A source electrode 230 and a drain electrode 232 spaced apart from eachother are formed on the semiconductor layer 226. In addition, a dataline (not shown), which is electrically connected to the sourceelectrode 230 and crosses the gate line to define a pixel region, isformed.

The gate electrode 222, the semiconductor layer 226, the sourceelectrode 230 and the drain electrode 232 constitute the TFT Tr.

A passivation layer 234, which includes a drain contact hole 236exposing the drain electrode 232, is formed on the TFT Tr.

A pixel electrode 240, which is connected to the drain electrode 232through the drain contact hole 236, and a common electrode 242, which isalternately arranged with the pixel electrode 240, are formed on thepassivation layer 234.

A second buffer layer 252 is formed on the second flexible substrate250, and a black matrix 254, which shields a non-display region such asthe TFT Tr, the gate line and the data line, is formed on the secondbuffer layer 252. In addition, a color filter layer 256, whichcorresponds to the pixel region, is formed on the second buffer layer252. The second buffer layer 252 and the black matrix 254 may beomitted.

The first and second flexible substrates 212 and 250 are attached withthe liquid crystal layer 260 therebetween. The liquid crystal molecules262 of the liquid crystal layer 260 is driven by an electric fieldbetween the pixel and common electrode 240 and 242.

Although not shown, first and second alignment layers may be formed overthe first and second flexible substrates 212 and 250 to be adjacent tothe liquid crystal layer 260. In addition, first and second polarizationplates, which have perpendicular transmission axes, may be attached toan outer side of each of the first and second flexible substrates 212and 250. Moreover, a flexible backlight unit may be disposed under thefirst flexible substrate 212 to provide light.

Referring again to FIGS. 3A and 3B, the backplate 180 is disposed underthe display panel 110 such that the display panel 110 is supported bythe backplate 180. For example, the backplate 180 may be attached to theflexible substrate 112 using an adhesive layer (not shown).

The backplate 180 includes the first and second soft layers 182 and 186and the hard layer 184 between the first and second soft layers 182 and186. Namely, the backplate 180 has a triple-layered structure.

Alternatively, the backplate 180 may further include another soft layerand/or another hard layer. For example, at least one of the first andsecond soft layers 182 and 186 and the hard layer 184 may have adouble-layered structure including two different material layers.

The hard layer 184 includes a material having a Young's modulus value(i.e., elastic modulus value) larger than that of the first and secondsoft layers 182 and 186. Namely, the hard layer 184 has a high stiffnessthan the first and second soft layers 182 and 186. For example, each ofthe first and second soft layers 182 and 186 may have the modulus valueof about 1 to about 20 MPa, and the hard layer 184 may have the modulusvalue of about 10 to about 100 GPa.

Each of the first and second soft layers 182 and 186 may be formed ofone of polyurethane (PU), thermoplastic polyurethane (TPU), polyaramide(PA), rubber and silicon (Si). The hard layer 184 may be formed of ametal (e.g., stainless-steel (SUS)) or a polymer (e.g.,polymethylmetacrylate (PMMA), polycarbonate (PC), polyvinylalcohol(PVA), acrylonitrile-butadiene-styrene (ABS), polyethylene terephthalate(PET)).

The second soft layer 186 is closer to the display panel 110 than thefirst soft layer 182 and the hard layer 184. Namely, the second softlayer 186 is positioned between the display panel 110 and the hard layer184.

A lower surface 182 a of the first soft layer 182 is flat, and an uppersurface 182 b of the first soft layer 182 has a curved shape. Namely,with respect to a horizontal plane, the upper surface 182 b of the firstsoft layer 182 has a downwardly concave shape.

Accordingly, the first soft layer 182 has a first thickness t1 at acenter portion and a second thickness t2, which is larger than the firstthickness t1, at an edge portion.

Since the first soft layer 182 is at the bottom of the display device100, it is preferred that the lower surface 182 a of the first softlayer 182 is flat. However, the shape of the lower surface 182 a is notlimited thereto.

The hard layer 184 is disposed on the upper surface 182 b of the firstsoft layer 182 and has a curved shape. Namely, a center portion of thehard layer 184 and an edge portion of the hard layer 184 have adifference in a distance from a reference line, e.g., the lower surface182 a of the first soft layer 182. The center portion of the hard layer184 may have a first distance from the reference line, and the edgeportion of the hard layer 184 may have a second distance, which islarger than the first distance, from the reference line.

With respect to a horizontal plane, a lower surface 184 a of the hardlayer 184 has a downwardly convex shape. The upper surface 182 b of thefirst soft layer 182 and the lower surface 184 a of the hard layer 184may have substantially the same curvature. Accordingly, the entire lowersurface 184 a of the hard layer 184 and the entire upper surface 182 bof the first soft layer 182 may come into contact with each other.

With respect to the horizontal plane, an upper surface 184 b of the hardlayer 184 has a downwardly concave shape. The upper surface 184 b of thehard layer 184 and the lower surface 184 a of the hard layer 184 mayhave the same curvature such that the hard layer 184 may have asubstantially uniform third thickness t3 at a center portion and an edgeportion.

Alternatively, the upper surface 184 b of the hard layer 184 and thelower surface 184 a of the hard layer 184 may have a difference in acurvature such that the hard layer 184 may have a thickness deviation.In other words, the lower surface 184 a of the hard layer 184 has afirst curvature along a first direction, i.e., a direction to the firstsoft layer 182, and the upper surface 184 b of the hard layer 184 has asecond curvature, which is different from the first curvature, along thefirst direction.

The second soft layer 186 is positioned on the upper surface 184 b ofthe hard layer 184. An upper surface 186 b of the second soft layer 186is flat, and a lower surface 186 a of the second soft layer 186 has acurved shape. In other words, with respect to a horizontal plane, thelower surface 186 a of the second soft layer 186 has a downwardly convexshape. Accordingly, the second soft layer 186 has a fourth thickness t4at a center portion and a fifth thickness t5, which is smaller than thefourth thickness t4, at an edge portion.

The lower surface 186 a of the second soft layer 186 may havesubstantially the same curvature as the upper surface 184 b of the hardlayer 184. Accordingly, the lower surface 186 a of the second soft layer186 and the upper surface 184 b of the hard layer 184 may entirelycontact.

In FIG. 3B, the upper surface 182 b of the first soft layer 182, thelower and upper surfaces 184 a and 184 b of the hard layer 184 and thelower surface 186 a of the second soft layer 186 have the samecurvature. Alternatively, the upper surface 182 b of the first softlayer 182 and the lower surface 184 a of the hard layer 184 may have afirst curvature, and the upper surface 184 b of the hard layer 184 andthe lower surface 186 a of the second soft layer 186 may have a secondcurvature being different from the first curvature.

The hard layer 184 has a relatively thin thickness such that therestoring property of the backplate 180 is improved. In other words, thethird thickness t3 of the hard layer 184 is smaller than the secondthickness t2 at the edge portion of the first soft layer 182 and thefourth thickness t4 at the center portion of the second soft layer 186.

Since the second soft layer 186 is a uppermost element of the backplate180, it is preferred that the upper surface 186 b of the second softlayer 186 is flat. However, the shape of the upper surface 186 b of thesecond soft layer 186 is not limited thereto.

Since the backplate 180 includes the hard layer 184 having a highmodulus value, the backplate 180 has a high restoring force of thebackplate 180. Accordingly, despite a reduced thickness, the restoringproperty of the backplate 180 is improved.

However, when the backplate 180 has a single layer of a high modulusvalue material, the folding stress is concentrated on the backplate 180such that there is a problem in the restoration of the backplate 180,i.e., the unfolding operation. Namely, since an elastic deformationregion of the hard layer 184, which is formed of a high modulus valuematerial, is narrow, the restoration of the hard layer 184 after thefolding operation is very difficult. Accordingly, the backplate 180 isnot unfolded after being folded and instead retains the unfolded shape.

However, the backplate 180 includes not only the hard layer 184 but alsothe first and second soft layers 182 and 186, and each of the first andsecond soft layers 182 and 186 has a thickness deviation. Namely, thehard layer 184 has a curved shape such that the folding stress isreduced and the restoring property of the backplate 180 is improved.

For example, when the foldable display device is folded, the length ofthe display device is increased such that the folding stress isconcentrated on a center portion of the backplate. However, since thehard layer 184 has the curved shape with increased length compared to aflat configuration, the bending stress is distributed over a wider areaof the hard layer 184. Accordingly, the folding stress in the centerportion of the hard layer 184 is reduced, and the restoring property ofthe backplate 180 is improved.

In addition, the backplate 180 has a flat bottom surface and a flat topsurface due to the configuration of the first and second soft layers 182and 186, the combination with other elements and the stability of thefabricating process are secured.

The cover window 190 protects the display panel 110 from outer impactsand prevents damages (e.g., scratches) on the display panel 110. Thecover window 190 may be omitted.

Although not shown, a touch panel may be disposed between the displaypanel 110 and the cover window 190. On the other hand, the foldabledisplay device 100 including the backplate 180, where the hard layer 184has a downwardly curved shape, is folded toward the display panel 110.Alternatively, when the foldable display device 100 is folded toward thebackplate 180, the hard layer 184 of the backplate 180 may have anupwardly curved shape. In this instance, the first soft layer 182 mayhave larger thickness in a center portion than an edge portion, and thesecond soft layer 186 may have larger thickness in an edge portion thana center portion.

As mentioned above, since the foldable display device 100 includes thebackplate 180 including the hard layer 184 having a curved shape and thefirst and second soft layers 182 and 186 attached to opposite sides ofthe hard layer 184, the restoring force the foldable display device 100is increased. Accordingly, a thin foldable display device 100 withenhanced folding and unfolding properties is provided.

FIG. 5A is a schematic cross-sectional view of a foldable display deviceaccording to an embodiment. FIG. 5B is a schematic cross-sectional viewof a backplate according to the embodiment of FIG. 5A. As shown in FIGS.5A and 5B, a foldable display device 300 includes a display panel 310, abackplate 380, and a cover window 390 disposed on the display panel 310.The backplate 380 is disposed under the display panel 310 and includes afirst soft layer 382, a hard layer 384 (also referred to as a “non-flatlayer” herein) and a second soft layer 386.

The display panel 310 includes a flexible substrate 312 and a displaypart 314 on the flexible substrate 312. For example, the flexiblesubstrate 312 may be a polyimide substrate, and the display panel 310may be an emitting diode panel or a liquid crystal panel.

When the display panel 310 is used as the emitting diode panel, as shownin FIG. 4A, the display panel 310 may include the TFT Tr as a drivingelement and an emitting diode D. On the other hand, when the displaypanel 310 is the liquid crystal panel, as shown in FIG. 4B, the displaypanel 310 may includes the first and second flexible substrates 212 and250, the liquid crystal layer 260 therebetween, the pixel electrode 240and the common electrode 242.

Referring again to FIGS. 5A and 5B, the backplate 380 is disposed underthe display panel 310 such that the display panel 310 is supported bythe backplate 380. For example, the backplate 380 may be attached to theflexible substrate 312 using an adhesive layer (not shown).

The backplate 380 includes the first and second soft layers 382 and 386and the hard layer 384 between the first and second soft layers 382 and386. Namely, the backplate 380 has a triple-layered structure.

Alternatively, the backplate 380 may further include another soft layerand/or another hard layer. For example, at least one of the first andsecond soft layers 382 and 386 and the hard layer 384 may have adouble-layered structure including two different material layers.

The hard layer 384 includes a material having a modulus value largerthan that of the first and second soft layers 382, 386. Other than theshape of the hard layer 384, the hard layer 384 is substantially thesame as the hard layer 184. Similarly, the first and second soft layers382, 386 are substantially the same as the first and second soft layers182, 186. Therefore, detailed description on properties and material ofthe hard layer 384, the first soft layer 382 and the second layer 386are omitted herein for the sake of brevity.

A lower surface 382 a of the first soft layer 382 is flat, and an uppersurface 382 b of the first soft layer 382 has a first “V” shape.Accordingly, the first soft layer 382 has a first thickness t1 at acenter portion and a second thickness t2, which is larger than the firstthickness t1, at an edge portion.

Since the first soft layer 382 is at the bottom of the display device300, it is preferred that the lower surface 382 a of the first softlayer 382 is flat. However, the shape of the lower surface 382 a is notlimited thereto.

The hard layer 384 is disposed on the upper surface 382 b of the firstsoft layer 382 and has a second “V” shape. Namely, a center portion ofthe hard layer 384 and an edge portion of the hard layer 384 have adifference in a distance from a reference line, e.g., the lower surface382 a of the first soft layer 382. The center portion of the hard layer384 may have a first distance from the reference line, and the edgeportion of the hard layer 384 may have a second distance, which islarger than the first distance, from the reference line.

The upper surface 382 b of the first soft layer 382 and the lowersurface 384 a of the hard layer 384 may have the same inner angle.Namely, the upper surface 382 b of the first soft layer 382 has a firstinner angle θ1, and the lower surface 384 a of the hard layer 384 has asecond inner angle θ2 being equal to the first inner angle θ1.Accordingly, the lower surface 384 a of the hard layer 384 and the uppersurface 382 b of the first soft layer 382 entirely contact.

An upper surface 384 b of the hard layer 384 has a third “V” shape. Theupper surface 384 b of the hard layer 384 has the same inner angle asthe lower surface 384 a of the hard layer 384 such that the hard layer384 has a substantially uniform thickness, i.e., a third thickness t3,in the center portion and the edge portion. Namely, the upper surface384 b of the hard layer 384 has a third inner angle θ3 substantiallyequal to the second inner angle θ2 of the lower surface 384 a of thehard layer 384.

Alternatively, the upper surface 384 b of the hard layer 384 and thelower surface 384 a of the hard layer 384 may have a different innerangle such that there may be a thickness deviation in the hard layer384.

The second soft layer 386 is positioned on the upper surface 384 b ofthe hard layer 384. An upper surface 386 b of the second soft layer 386is flat, and a lower surface 386 a of the second soft layer 386 has afourth “V” shape. Accordingly, the second soft layer 386 has a fourththickness t4 at the center portion and a fifth thickness t5, which issmaller than the fourth thickness t4, at the edge portion.

The lower surface 386 a of the second soft layer 386 has substantiallythe same inner angle as the upper surface 384 b of the hard layer 384.Namely, the lower surface 386 a of the second soft layer 386 has afourth inner angle θ4 substantially equal to the third inner angle θ3 ofthe upper surface 384 b of the hard layer 384. Accordingly, the entirelower surface 386 a of the second soft layer 386 and the entire uppersurface 384 b of the hard layer 384 come into contact with each other.

In FIG. 5, the upper surface 382 b of the first soft layer 382, thelower and upper surfaces 384 a and 384 b of the hard layer and the lowersurface 386 a of the second soft layer 386 have the same inner angle.

Alternatively, the upper surface 382 b of the first soft layer 382 andthe lower surface 384 a of the hard layer 384 may have the same innerangle, and the upper surface 384 b of the hard layer 384 and the lowersurface 386 a of the second soft layer 386 may have the same inner anglebeing different from the inner angle of the upper surface 382 b of thefirst soft layer 382 and the lower surface 384 a of the hard layer 384.

In addition, the upper surface 382 b of the first soft layer 382 and thelower surface 384 a of the hard layer 384 may have the “V” shape as FIG.5B, while the upper surface 384 b of the hard layer 384 and the lowersurface 386 a of the second soft layer 386 may have the curved shape asshown in FIG. 3B. Alternatively, the upper surface 382 b of the firstsoft layer 382 and the lower surface 384 a of the hard layer 384 mayhave the curved shape as FIG. 3B, while the upper surface 384 b of thehard layer 384 and the lower surface 386 a of the second soft layer 386may have the “V” shape as shown in FIG. 5B.

The hard layer 384 has a relatively thin thickness such that therestoring property of the backplate 380 is improved. In other words, thethird thickness t3 of the hard layer 384 is smaller than the secondthickness t2 at the edge portion of the first soft layer 382 and thefourth thickness t4 at the center portion of the second soft layer 386.

Since the second soft layer 386 is an uppermost element of the backplate380, it is preferred that the upper surface 386 b of the second softlayer 386 is flat. However, the shape of the upper surface 386 b of thesecond soft layer 386 is not limited thereto.

As mentioned above, the backplate 380 includes the hard layer 384 havinga high modulus value, and the first and second soft layers 382 and 386,which are attached to the lower and upper surfaces 384 a and 384 b ofthe hard layer 384, respectively, have the thickness deviation. Namely,the hard layer 384 has the “V” shape such that the folding stress of thebackplate 380 is reduced and the restoring property of the backplate 380is improved.

In addition, the backplate 380 has a flat bottom surface and a flat topsurface due to the first and second soft layers 382 and 386, thecombination with other elements and the stability of the fabricatingprocess are secured.

The cover window 390 protects the display panel 310 from outer impactsand prevents damages, e.g., scratches, on the display panel 310. Thecover window 390 may be omitted.

Although not shown, a touch panel may be disposed between the displaypanel 310 and the cover window 390.

On the other hand, the foldable display device 300 including thebackplate 380, where the hard layer 384 has the “V” shape, is foldedtoward the display panel 310. As shown above with reference to FIG. 2B,downward plastic deformation tends to appear along the center portion ofthe back cover. Therefore, the hard layer 384 is pre-formed with “V”shape at the center so as to prevent downward plastic deformation fromoccurring. Because the center portion is pre-formed with a downwardshape, the center portion of the hard layer 384 is less likely toexperience further plastic deformation by repeated folding and unfoldingof the back cover 380.

Alternatively, when the foldable display device 300 is folded toward thebackplate 380, the hard layer 384 of the backplate 380 may have areverse “V” shape. In this instance, the first soft layer 382 may havelarger thickness in the center portion than the edge portion, and thesecond soft layer 386 may have larger thickness in the edge portion thanthe center portion.

As mentioned above, since the foldable display device 300 includes thebackplate 380 including the hard layer 184 having the “V” shape and thefirst and second soft layers 382 and 386 attached to opposite sides ofthe hard layer 384, the restoring force the foldable display device 300is increased. Accordingly, a thin foldable display device 300 withenhanced folding and unfolding properties is provided.

FIG. 6A is a schematic cross-sectional view of a foldable display deviceaccording to an embodiment. FIG. 6B is a schematic cross-sectional viewof a backplate according to FIG. 6A. As shown in FIGS. 6A and 6B, afoldable display device 400 includes a display panel 410, a backplate480, and a cover window 490 disposed on the display panel 410. Thebackplate 480 is disposed under the display panel 410 and includes afirst soft layer 482, a hard layer 484 (also referred to as a “non-flatlayer” herein) and a second soft layer 486.

The display panel 410 includes a flexible substrate 412 and a displaypart 414 on the flexible substrate 412. For example, the flexiblesubstrate 412 may be a polyimide substrate, and the display panel 410may be an emitting diode panel or a liquid crystal panel.

When the display panel 410 is the emitting diode panel, as shown in FIG.4A, the display panel 410 may include the TFT Tr as a driving elementand an emitting diode D. On the other hand, when the display panel 410is the liquid crystal panel, as shown in FIG. 4B, the display panel 410may includes the first and second flexible substrates 212 and 250, theliquid crystal layer 260 therebetween, the pixel electrode 240 and thecommon electrode 242.

Referring again to FIGS. 6A and 6B, the backplate 480 is disposed underthe display panel 410 such that the display panel 410 is supported bythe backplate 480. For example, the backplate 480 may be attached to theflexible substrate 412 using an adhesive layer (not shown).

The backplate 480 includes the first and second soft layers 482 and 486and the hard layer 484 between the first and second soft layers 482 and486. Namely, the backplate 480 has a triple-layered structure.

Alternatively, the backplate 480 may further include another soft layerand/or another hard layer. For example, at least one of the first andsecond soft layers 482 and 486 and the hard layer 484 may have adouble-layered structure including two different material layers.

The hard layer 484 includes a material having a modulus value largerthan that of the first and second soft layers 482 and 486. Other thanthe shape of the hard layer 484, the hard layer 484 is substantially thesame as the hard layer 184. Similarly, the first and second soft layers482, 486 are substantially the same as the first and second soft layers182, 186. Therefore, detailed description on properties and material ofthe hard layer 484, the first soft layer 482 and the second layer 486are omitted herein for the sake of brevity.

The second soft layer 486 is closer to the display panel 410 than thefirst soft layer 482 and the hard layer 484. Namely, the second softlayer 486 is positioned between the display panel 410 and the hard layer484.

A lower surface 482 a of the first soft layer 482 is flat, and an uppersurface 482 b of the first soft layer 482 has a curved shape. Namely,with respect to a horizontal plane, the upper surface 482 b of the firstsoft layer 482 has a downwardly concave shape in a center portion CP andan upwardly convex shape in a first edge portion EP1.

Accordingly, the first soft layer 482 has a first thickness in thecenter portion CP, a second thickness t2, which is larger than the firstthickness t1, in the first edge portion EP1, and a third thickness t3,which is smaller than the second thickness t2, in a second edge portionEP2 at an outer side of the first edge portion EP1.

Since the first soft layer 482 is at the bottom of the display device400, it is preferred that the lower surface 482 a of the first softlayer 482 is flat. However, the shape of the lower surface 482 a is notlimited thereto.

The hard layer 484 is disposed on the upper surface 482 b of the firstsoft layer 482 and has a curved shape. A lower surface 484 a of the hardlayer 484 has a downwardly convex shape in the center portion CP and anupwardly concave shape in the first edge portion EP1.

Namely, in the center portion CP, the lower surface 484 a of the hardlayer 484 has a first curvature along a first direction, i.e., adirection to the first soft layer 482, and an upper surface 484 b of thehard layer 484 has a second curvature, which is equal to or differentfrom the first curvature, along the first direction. In addition, in thefirst edge portion EP1, the lower surface 484 a of the hard layer 484has a third curvature along a second direction, which is opposite to thefirst direction, i.e., a direction to the second soft layer 486, and theupper surface 484 b of the hard layer 484 has a fourth curvature, whichis equal to or different from the third curvature, along the seconddirection.

In other words, the hard layer 484 has a difference in a distance from areference line, e.g., the lower surface 482 a of the first soft layer482. For example, from the reference line, a distance of the hard layer484 in the center portion CP and the second edge portion EP2 may besmaller than that of the hard layer 484 in the first edge portion EP1.

The upper surface 482 b of the first soft layer 482 and the lowersurface 484 a of the hard layer 484 may have substantially the samecurvature. Accordingly, the entire lower surface 484 a of the hard layer484 and the entire upper surface 482 b of the first soft layer 482 maycome into contact with each other.

The upper surface 484 b of the hard layer 484 has a downwardly concaveshape in the center portion CP and an upwardly convex shape in the firstedge portion EP1.

The upper surface 484 b of the hard layer 484 and the lower surface 484a of the hard layer 484 may have the same curvature such that the hardlayer 484 may have a substantially uniform fourth thickness t4 at thecenter portion CP and the first and second edge portions EP1 and EP2.

Alternatively, the upper surface 484 b of the hard layer 484 and thelower surface 484 a of the hard layer 484 may have a difference in acurvature such that the hard layer 484 may have a thickness deviation.

The second soft layer 486 is positioned on the upper surface 484 b ofthe hard layer 484. An upper surface 486 b of the second soft layer 486is flat, and a lower surface 486 a of the second soft layer 486 has acurved shape.

The lower surface 486 a of the second soft layer 486 has a downwardlyconvex shape in the center portion CP and an upwardly concave shape inthe first edge portion EP1. Accordingly, the second soft layer 486 has afifth thickness in the center portion CP, a sixth thickness t6, which issmaller than the fifth thickness t5, in the first edge portion EP1, anda seventh thickness t7, which is larger than the sixth thickness t6, inthe second edge portion EP2 at an outer side of the first edge portionEP1.

The lower surface 486 a of the second soft layer 486 may havesubstantially the same curvature as the upper surface 484 b of the hardlayer 484. Accordingly, the lower surface 486 a of the second soft layer486 and the upper surface 484 b of the hard layer 484 may contact overtheir entire surfaces.

In FIG. 6B, the upper surface 482 b of the first soft layer 482, thelower and upper surfaces 484 a and 484 b of the hard layer 484 and thelower surface 486 a of the second soft layer 486 have the samecurvature. Alternatively, the upper surface 482 b of the first softlayer 482 and the lower surface 484 a of the hard layer 484 may have afirst curvature, and the upper surface 484 b of the hard layer 484 andthe lower surface 486 a of the second soft layer 486 may have a secondcurvature being different from the first curvature.

The hard layer 484 has a relatively thin thickness such that therestoring property of the backplate 480 is improved. In other words, thefourth thickness t4 of the hard layer 484 is smaller than the secondthickness t2 at the first edge portion EP1 of the first soft layer 482and the fifth thickness t5 at the center portion CP of the second softlayer 486.

Since the second soft layer 486 is an uppermost element of the backplate480, it is preferred that the upper surface 486 b of the second softlayer 486 is flat. However, the shape of the upper surface 486 b of thesecond soft layer 486 is not limited thereto.

As mentioned above, the backplate 480 includes the hard layer 484 havinga high modulus value, and the first and second soft layers 482 and 486,which are attached to the lower and upper surfaces 484 a and 484 b ofthe hard layer 484, respectively, have the thickness deviation. Namely,the hard layer 484 has a wave shape or a saw-tooth shape such that thefolding stress of the backplate 480 is reduced and the restoringproperty of the backplate 480 is improved.

In other words, since the hard layer 484 has a downwardly curved shapein the center portion CP and an upwardly curved shape in the first edgeportion EP1, a length increase in the center portion CP of the hardlayer 484 by the folding operation is further reduced. Accordingly, thefolding stress on the center portion CP of the hard layer 484 is furtherreduced, and the restoring property of the backplate 480 is furtherimproved.

In addition, the backplate 480 has a flat bottom surface and a flat topsurface due to the first and second soft layers 482 and 486, thecombination with other elements and the stability of the fabricatingprocess are secured.

The cover window 490 protects the display panel 410 from outer impactsand prevents damages, e.g., scratches, on the display panel 410. Thecover window 490 may be omitted.

Although not shown, a touch panel may be disposed between the displaypanel 410 and the cover window 490.

On the other hand, the foldable display device 400 including thebackplate 480, where the hard layer 484 has the downwardly curved shapein the center portion CP at a folding region, is folded toward thedisplay panel 410.

Alternatively, when the foldable display device 400 is folded toward thebackplate 480, the hard layer 484 of the backplate 480 may have anupwardly curved shape in the center portion CP. In this instance, thehard layer 484 may have a downwardly curved shape in the first edgeportion EP1. Moreover, the first soft layer 482 may have largerthickness in the center portion CP and the second edge portion EP2 thanthe first edge portion EP1, and the second soft layer 486 may havesmaller thickness in the center portion CP and the second edge portionEP2 than the first edge portion EP1.

As mentioned above, since the foldable display device 400 includes thebackplate 480 including the hard layer 484 having a curved shape, i.e.,a wave shape or a taw-tooth shape, and the first and second soft layers482 and 486 attached to opposite sides of the hard layer 484, therestoring force the foldable display device 400 is increased.Accordingly, a thin foldable display device 400 with enhanced foldingand unfolding properties is provided. As shown above with reference toFIG. 2B, downward plastic deformation tends to appear along the centerportion of the back cover. Therefore, the hard layer 484 is pre-formedwith a downward curved center so as to prevent downward plasticdeformation from occurring. Because the center portion is pre-formedwith a downward shape, the center portion of the hard layer 484 is lesslikely to experience further plastic deformation by repeated folding andunfolding of the back cover 480.

FIG. 7A is a schematic cross-sectional view of a foldable display deviceaccording to an embodiment. FIG. 7B is a schematic cross-sectional viewof a backplate of FIG. 7A.

As shown in FIGS. 7A and 7B, a foldable display device 500 includes adisplay panel 510, a backplate 580, and a cover window 590 disposed onthe display panel 510. A backplate 580 is disposed under the displaypanel 510 and includes a first soft layer 582, a hard layer 584 (alsoreferred to as a “non-flat layer” herein) and a second soft layer 586.

The display panel 510 includes a flexible substrate 512 and a displaypart 514 on the flexible substrate 512. For example, the flexiblesubstrate 512 may be a polyimide substrate, and the display panel 510may be an emitting diode panel or a liquid crystal panel.

When the display panel 510 is the emitting diode panel, as shown in FIG.4A, the display panel 510 may include the TFT Tr as a driving elementand an emitting diode D. On the other hand, when the display panel 510is the liquid crystal panel, as shown in FIG. 4B, the display panel 510may includes the first and second flexible substrates 212 and 250, theliquid crystal layer 260 therebetween, the pixel electrode 240 and thecommon electrode 242.

Referring again to FIGS. 7A and 7B, the backplate 580 is disposed underthe display panel 510 such that the display panel 510 is supported bythe backplate 580. For example, the backplate 580 may be attached to theflexible substrate 512 using an adhesive layer (not shown).

The backplate 580 includes the first and second soft layers 582 and 586and the hard layer 584 between the first and second soft layers 582 and586. Namely, the backplate 580 has a triple-layered structure.

Alternatively, the backplate 580 may further include another soft layerand/or another hard layer. For example, at least one of the first andsecond soft layers 582 and 586 and the hard layer 584 may have adouble-layered structure including two different material layers.

The hard layer 584 includes a material having a modulus value largerthan that of the first and second soft layers 582 and 586. Other thanthe shape of the hard layer 584, the hard layer 584 is substantially thesame as the hard layer 184. Similarly, the first and second soft layers582, 586 are substantially the same as the first and second soft layers182, 186. Therefore, detailed description on properties and material ofthe hard layer 584, the first soft layer 582 and the second layer 586are omitted herein for the sake of brevity.

The second soft layer 586 is closer to the display panel 510 than thefirst soft layer 582 and the hard layer 584. Namely, the second softlayer 586 is positioned between the display panel 510 and the hard layer584.

A lower surface 582 a of the first soft layer 582 is flat, and an uppersurface 582 b of the first soft layer 582 has a gull-like shape. Namely,the upper surface 582 b of the first soft layer 582 has a “V” shape in acenter portion CP and a reverse “V” shape in a first edge portion EP1.

Accordingly, the first soft layer 582 has a first thickness in thecenter portion CP, a second thickness t2, which is larger than the firstthickness t1, in the first edge portion EP1, and a third thickness t3,which is smaller than the second thickness t2, in a second edge portionEP2 at an outer side of the first edge portion EP1.

Since the first soft layer 582 is at the bottom of the display device500, it is preferred that the lower surface 582 a of the first softlayer 582 is flat. However, the shape of the lower surface 582 a is notlimited thereto.

The hard layer 584 is disposed on the upper surface 582 b of the firstsoft layer 582 and has a gull-like shape. A lower surface 584 a of thehard layer 584 has a “V” shape in the center portion CP and a reverse“V” shape in the first edge portion EP1.

In other words, the hard layer 584 has a difference in a distance from areference line, e.g., the lower surface 582 a of the first soft layer582. For example, from the reference line, a distance of the hard layer584 in the center portion CP and the second edge portion EP2 may besmaller than that of the hard layer 584 in the first edge portion EP1.

The upper surface 582 b of the first soft layer 582 and the lowersurface 584 a of the hard layer 584 may have substantially the sameshape. Namely, in each of the center portion CP and the first edgeportion EP1, an inner angle of the upper surface 582 b of the first softlayer 582 may be equal to that of the lower surface 584 a of the hardlayer 584. (θ1=θ2, θ5=θ6) Accordingly, the entire lower surface 584 a ofthe hard layer 584 and the entire upper surface 582 b of the first softlayer 582 may come into contact with each other.

The upper surface 584 b of the hard layer 584 and the lower surface 584a of the hard layer 584 may have the same gull-like shape. Namely, ineach of the center portion CP and the first edge portion EP1, an innerangle of each of the lower and upper surfaces 584 a and 584 b of thehard layer 584 may be equal. (θ2=θ3, θ6=θ7) Accordingly, the hard layer584 may have a substantially uniform fourth thickness t4 at the centerportion CP and the first and second edge portions EP1 and EP2.

Alternatively, the upper surface 584 b of the hard layer 584 and thelower surface 584 a of the hard layer 584 may have a difference in aninner angle such that the hard layer 584 may have a thickness deviation.

The second soft layer 586 is positioned on the upper surface 584 b ofthe hard layer 584. An upper surface 586 b of the second soft layer 586is flat, and a lower surface 586 a of the second soft layer 586 has agull-like shape. Accordingly, the second soft layer 586 has a fifththickness in the center portion CP, a sixth thickness t6, which issmaller than the fifth thickness t5, in the first edge portion EP1, anda seventh thickness t7, which is larger than the sixth thickness t6, inthe second edge portion EP2 at an outer side of the first edge portionEP1.

The lower surface 586 a of the second soft layer 586 may havesubstantially the same inner angle as the upper surface 584 b of thehard layer 584. Namely, in each of the center portion CP and the firstedge portion EP1, an inner angle of the lower surface 586 a of thesecond soft layer 586 may be equal to that of the upper surface 584 b ofthe hard layer 584. (θ4=θ3, θ8=θ7) Accordingly, the entire lower surface586 a of the second soft layer 586 and the entire upper surface 584 b ofthe hard layer 584 may come into contact with each other.

In FIG. 7B, the upper surface 582 b of the first soft layer 582, thelower and upper surfaces 584 a and 584 b of the hard layer 584 and thelower surface 586 a of the second soft layer 586 have the same innerangle. Alternatively, the upper surface 582 b of the first soft layer582 and the lower surface 584 a of the hard layer 584 may have the sameinner angle, and the upper surface 584 b of the hard layer 584 and thelower surface 586 a of the second soft layer 586 may have a differentinner angel from the upper surface 582 b of the first soft layer 582 andthe lower surface 584 a of the hard layer 584. (θ1=θ2, θ5=θ6, θ3=θ4,θ7=θ8, θ1≠03, θ5≠θ7)

In addition, the upper surface 582 b of the first soft layer 582 and thelower surface 584 a of the hard layer 584 may have the gull-like shapeas FIG. 7B, and the upper surface 584 b of the hard layer 584 and thelower surface 586 a of the second soft layer 586 may have the wave shapeor the taw-tooth shape as FIG. 6B. Alternatively, the upper surface 582b of the first soft layer 582 and the lower surface 584 a of the hardlayer 584 may have the wave shape or the taw-tooth shape as FIG. 6B, andthe upper surface 584 b of the hard layer 584 and the lower surface 586a of the second soft layer 586 may have the gull-like shape as FIG. 7B.

Moreover, each of the upper surface 582 b of the first soft layer 582,the lower and upper surfaces 584 a and 584 b of the hard layer 584 andthe lower surface 586 a of the second soft layer 586 may an angularshape, i.e., the “V” shape, in the center portion CP as FIG. 7B and thecurved shape in the first edge portion EP1 as FIG. 6B. Alternatively,each of the upper surface 582 b of the first soft layer 582, the lowerand upper surfaces 584 a and 584 b of the hard layer 584 and the lowersurface 586 a of the second soft layer 586 may the curved shape in thecenter portion CP as FIG. 6B and the angular shape, i.e., the “V” shape,in the first edge portion EP1 as FIG. 7B.

The hard layer 584 has a relatively thin thickness such that therestoring property of the backplate 580 is improved. In other words, thefourth thickness t4 of the hard layer 584 is smaller than the secondthickness t2 at the first edge portion EP1 of the first soft layer 582and the fifth thickness t5 at the center portion CP of the second softlayer 586.

Since the second soft layer 586 is a uppermost element of the backplate580, it is preferred that the upper surface 586 b of the second softlayer 586 is flat. However, the shape of the upper surface 586 b of thesecond soft layer 586 is not limited thereto.

As mentioned above, the backplate 580 includes the hard layer 584 havinga high modulus value, and the first and second soft layers 582 and 586,which are attached to the lower and upper surfaces 584 a and 584 b ofthe hard layer 584, respectively, have the thickness deviation. Namely,the hard layer 584 has a gull-like shape such that the folding stress ofthe backplate 580 is reduced and the restoring property of the backplate580 is improved.

In other words, since the hard layer 584 has a “V” shape in the centerportion CP and a reverse “V” shape in the first edge portion EP1, alength increase in the center portion CP of the hard layer 584 by thefolding operation is further reduced. Accordingly, the folding stress onthe center portion CP of the hard layer 584 is further reduced, and therestoring property of the backplate 580 is further improved.

As shown above with reference to FIG. 2B, downward plastic deformationtends to appear along the center portion of the back cover. Therefore,the hard layer 584 is pre-formed with “V” shape at the center so as toprevent downward plastic deformation from occurring. Because the centerportion is pre-formed with a downward shape, the center portion of thehard layer 584 is less likely to experience further plastic deformationby repeated folding and unfolding of the back cover 580.

In addition, the backplate 580 has a flat bottom surface and a flat topsurface due to the first and second soft layers 582 and 586, thecombination with other elements and the stability of the fabricatingprocess are secured.

The cover window 590 protects the display panel 510 from outer impactsand prevents damages, e.g., scratches, on the display panel 510. Thecover window 590 may be omitted.

Although not shown, a touch panel may be disposed between the displaypanel 510 and the cover window 590.

On the other hand, the foldable display device 500 including thebackplate 580, where the hard layer 584 has the “V” shape in the centerportion CP at a folding region, is folded toward the display panel 510.

Alternatively, when the foldable display device 500 is folded toward thebackplate 580, the hard layer 584 of the backplate 580 may have areverse “V” shape in the center portion CP and a “V” shape in the firstedge portion EP1. Moreover, the first soft layer 582 may have largerthickness in the center portion CP and the second edge portion EP2 thanthe first edge portion EP1, and the second soft layer 586 may havesmaller thickness in the center portion CP and the second edge portionEP2 than the first edge portion EP1.

As mentioned above, since the foldable display device 500 includes thebackplate 580 including the hard layer 584 having a gull-like shape, andthe first and second soft layers 582 and 586 attached to opposite sidesof the hard layer 584, the restoring force the foldable display device500 is increased. Accordingly, a thin foldable display device 500 withexcellent folding and unfolding properties is provided.

What is claimed is:
 1. A foldable display device, comprising: a displaypanel having a bottom surface; and a backplate disposed at a first sideof the display panel to enhance resilience of the foldable displaydevice, the backplate comprising: a first layer of first material havinga first elastic modulus, the first layer having a first top profile thatmatches a bottom profile of the display panel, a second layer of secondmaterial having a second elastic modulus, the second layer having asecond top profile, and a non-flat layer of third material having athird elastic modulus higher than the first elastic modulus and thesecond elastic modulus, the non-flat layer between the first layer andthe second layer, the non-flat layer having a top profile that matches abottom profile of the first layer and a bottom profile that matches thesecond top profile of the second layer, the top profile and the bottomprofile of the non-flat layer different from the first top profile ofthe first layer.
 2. The foldable display device of claim 1, wherein thefirst material is same as the second material.
 3. The foldable displaydevice of claim 1, wherein the top profile of the non-flat layer isconcaved with a predetermined radius of curvature and the bottom profileof the non-flat layer is convexed with the predetermined radius ofcurvature.
 4. The foldable display device of claim 1, wherein thenon-flat layer has a first inclined portion slanted downward towards acenter line of the non-flat layer along which the backplate is bent, anda second inclined portion connected to the first inclined portion andslanted downwards towards the center line.
 5. The foldable displaydevice of claim 1, wherein the non-flat layer comprises: a middleportion having a concave top surface and a convex bottom surface; andedge portions, each of the edge portions connected to an edge of themiddle portion, each of the edge portions having a convex top surfaceand a concave bottom surface.
 6. The foldable display device of claim 1,wherein the first top profile is flat and the bottom profile of thefirst layer is convex.
 7. The foldable display device of claim 1,wherein the non-flat layer has a same thickness at different portions ofthe non-flat layer.
 8. The foldable display device of claim 1, whereinthe non-flat layer has a first thickness at a first location of thenon-flat layer and a second thickness at a second location of thenon-flat layer.
 9. The foldable display device of claim 1, wherein thenon-flat layer is curved or bent towards a shape that results fromplastic deformation of the non-flat layer by repeated folding andunfolding of the backplate.
 10. The foldable display device of claim 1,wherein the display panel includes a light emitting diode, and whereinan image is displayed at a second side opposite to the first side. 11.The foldable display device of claim 5, wherein the concave top surfaceand the convex bottom surface of the middle portion are curved, and theconvex top surface and the concave bottom surface of each of the edgeportions are curved.
 12. The foldable display device of claim 5, whereinthe concave top surface and the convex bottom surface of the middleportion comprise a plurality of flat surfaces, and the convex topsurface and the concave bottom surface of each of the edge portions areflat surfaces.
 13. A backplate disposed at a side of a display panel toenhance resilience of the foldable display device, the backplatecomprising: a first layer of first material having a first elasticmodulus, the first layer having a first top profile that matches abottom profile of the display panel, a second layer of second materialhaving a second elastic modulus, the second layer having a second topprofile, and a non-flat layer of third material having a third elasticmodulus higher than the first elastic modulus and the second elasticmodulus, the non-flat layer between the first layer and the secondlayer, the non-flat layer having a top profile that matches a bottomprofile of the first layer and a bottom profile that matches the secondtop profile of the second layer, the top profile and the bottom profileof the non-flat layer different from the first top profile of the firstlayer.
 14. The backplate of claim 13, wherein the top profile of thenon-flat layer is concaved with a predetermined radius of curvature andthe bottom profile of the non-flat layer is convexed with thepredetermined radius of curvature.
 15. The backplate of claim 13,wherein the non-flat layer has a first inclined portion slanted downwardtowards a center line of the non-flat layer along which the backplate isbent, and a second inclined portion connected to the first inclinedportion and slanted downward towards the center line of the non-platlayer.
 16. The backplate of claim 13, wherein the non-flat layercomprises: a middle portion having a concave top surface and a convexbottom surface; and edge portions, each of the edge portions connectedto an edge of the middle portion, each of the edge portions having aconvex top surface and a concave bottom surface.
 17. The backplate ofclaim 13, wherein the first layer has a flat top surface and a convexbottom surface, the flat top surface secured to the display panel andthe convex bottom surface secured to a top surface of the non-flatlayer.
 18. The backplate of claim 13, wherein the non-flat layer has asame thickness at different portions of the non-flat layer.
 19. Thebackplate of claim 13, wherein the non-flat layer is curved or benttowards a shape that results from plastic deformation of the non-flatlayer by repeated folding and unfolding of the non-flat layer.